


got milk?

by avosettas



Category: Undertale (Video Game)
Genre: Coming Untouched, Crosstale Sans (Undertale), Crosstale Sans/Killer Sans (Undertale), Ecto-Breasts (Undertale), Ecto-Genitalia (Undertale), Killer Sans (Undertale) - Freeform, Lactation, M/M, Masturbation, Milking, Nipple Play, Weird Biology
Language: English
Status: Completed
Published: 2021-01-18
Updated: 2021-01-18
Packaged: 2021-03-16 06:16:36
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,318
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/28826568
Author URL: https://archiveofourown.org/users/avosettas/pseuds/avosettas
Summary: Cross's LV acts up. Killer milks it for all it's worth. Literally.
Relationships: Sans/Sans (Undertale)
Comments: 8
Kudos: 144





	got milk?

**Author's Note:**

  * For [zephyred](https://archiveofourown.org/users/zephyred/gifts).



> [head in hands] i cant believe i fucking wrote this,,, anyway nipple play? fucking hot thank u. this was 8 pages in google docs and most of it is just fucking. porn. also yes the title is completely necessary

With high LV comes physiological changes in the magical makeup of a monster’s body. Often, these changes are more pronounced, or otherwise harder to deal with, when the LV is gained quickly instead of over time. But most monsters in XTale hadn’t had any LV, and it was an understudied thing there. It didn’t matter anyway, though; all those monsters were gone, now, and the only one left was Cross.

He supposes it’s a good thing that he lives with three LV-ridden monsters, and a bookworm who knew the ins and outs of it well enough to give him a lecture on it. He probably could have done without the excruciating detail, and the pile of books Nightmare had given him on LV afterwards. 

Not that Cross wasn’t grateful; the day he gained his LV was one of the worst in his life. Even barring the emotional pain, his whole body had burned with each ~~murder~~ death, the bloodlust practically uncontrollable despite the sensation of fire in his marrow. 

That was what going from LV 1 to LV 12 in a matter of hours did to you, though. Looking back, Cross can only guess that it was good that he was distracted by his fragmenting code, and the maddening grief as his world imploded around him.

Now, however, there were no distractions. 

High LV led to pent up magic; Cross had known this, of course - anyone who’d known Dust for more than a week knew that, considering he had such high LV that it made his magic overactive and unpredictable at the best times. But Dust also was at such a high LV that checking his stats only showed **20+** now when they were checked. 

Maybe it’s for the better that Cross is still able to control his magic, but he almost wishes that it had sent him into a frenzy like Dust’s magic did. What’s happening to him now feels like a heat, though he knows for a fact he’s not due for his next cycle for at least two months. 

It feels strange, too. The pressure is built up beneath his ribs, as if it’s in his very soul, rather than in his pelvis like it would be during a heat. He’s read about human “heart attacks”, with their symptoms of feeling like their chest is being squeezed like a vice; if he had that sort of physiology, he’d be worried that that’s what was happening. 

Cross tries to relax, but the bedspread beneath him feels scratchy on his arms, and his shirt is even worse. The open window does nothing to calm him; he’s shivering despite the sweat on his face, and he thinks for a moment that maybe he _has_ entered heat early, but dismisses it just as quickly. 

It’s certainly something else; Cross knows his heats, predictable like clockwork, down to the way he forms a nest each time, beginning with a blanket spread on the floor and building on top of that. Not to mention that the burn of his LV is palpable, like he could reach beneath his ribs for his soul and _see_ the bloodlust in the feverishly beating organ. 

Briefly, he considers finding Dust or Killer, or even Nightmare, but dismisses the idea just as quick. Dust would be unhelpful at best, and begin panicking at worst; he was rather unpredictable, and it was best to try to keep him calm for his own sake. Killer is the most feasible idea, since he would probably be the nearest, but Cross loathes the idea of being vulnerable in front of him. He’d probably just flirt with Cross until he decided he’d had enough of Killer’s bullshit. And Nightmare would probably just point him towards some old tome, or worse, give him some sort of sex talk. 

He resigns himself to suffering in silence, pressing a hand to his sternum to try and ease the pain there, and while it eases the tension, it also makes him gasp pathetically. 

For some reason, his chest is _stupidly_ sensitive now, and Cross glares down at himself, as if it will help. But the pressure did help the aching there, and so he slips his hands beneath his shirt and presses them to his ribs. 

The result is unexpected, and _embarrassing_.

Without his conscious say-so, Cross’s ecto-body has come into being. His breasts feel heavy and it’s like the ache that had been beneath his ribs transferred to them. It’s not how they normally feel, and when he scoots up to lean against the wall, he thinks they seem _bigger_ , too. 

Cross snarls, though at what, he isn’t sure. He’s just _uncomfortable_ , leaning against the wall with his breasts feeling as though they’re trying to drag him right back down to the bed. Belatedly, he realizes his cunt has manifested too, and it already feels uncomfortably wet in his shorts. 

He bangs his skull against the wall, not hard enough to really hurt or do damage, but hard enough to ache a bit. He’s not sure what he’s trying to accomplish, though it’s certainly _not_ to attract attention. 

Because as he grumbles to himself, there’s a knock at his door. Cross manages to yell, “I’m not decent!” though his voice cracks embarrassingly as he does. 

And it’s not like that’s ever stopped Killer, either. He steps into the room despite Cross’s growl, and closes the door behind him, unconcerned. “sounded like you were havin’ some issues.” 

“I’m fine,” Cross says, but his voice is unsteady and Killer can see everything: his stupidly heavy breasts, his spread legs, trying to keep his shorts from getting any stickier… 

“mhm.” Killer is obviously unconvinced. He knows all of Cross’s tells by now, even the sexual ones; they’ve helped each other through heats for nearly a year now, which means, Cross supposes, that he’s glad that if _anyone_ has to see him like this, it’s Killer. 

“i can practically smell your lv actin’ up, criss-cross,” he says as he moves towards Cross, continuing before Cross can protest. “it’s the reason you’re lookin’ so tasty, too.” 

“I thought LV was supposed to make me angry,” Cross replies petulantly, “not… horny and… ugh.” His face feels like it’s burning in embarrassment, and Killer laughs, sitting beside him on the edge of the bed. 

“comes in a lotta ways,” he says, one hand moving to hold Cross’s cheek and caress it with a thumb. “sometimes it’s like heat. sometimes it’s like… this. ‘nd sometimes it’s like anger and rage. or depression. or, y’know, psychosis, like dusty.” 

Cross focuses on one bit. “Like ‘this’?” he asks weakly, unconsciously tilting his head to let Killer rub at his jaw. “It… feels like a heat to me.” 

Killer chuckles, removing his hand from Cross’s face and plucking at the hem of his shirt. “d’you want me to help, or d’you want me to explain?”

“Preferably both,” Cross replies, a little breathless as Killer fiddles with his shirt, knuckles occasionally touching his waist. Everything feels sensitive; even the brief touch feels nice. 

“‘course, criss-cross,” Killer grins, and pulls his shirt over his head. Cross shivers; the open window apparently had cooled the room, and he hadn’t noticed. 

He doesn’t think on that for long though, because he’s noticing how his ecto-body is _different_. His nipples seem huge, and it appears that he was right about his breasts looking bigger, because they are. 

Something drips from his right nipple, viscous and warm on his false flesh as Killer thumbs it away. As Cross shivers from the light touch, Killer says nonchalantly, “what’cha know about mammals, crossy?” 

“Wh-what?” 

“mammals,” Killer repeats, resting one hand on Cross’s hip and the other on his stomach. Cross twitches beneath the touch, and Killer grins, rubbing the tense false muscles there. “basically, when they’re pregnant, they produce milk to nurse their young on, right? somethin’ about hormones, i dunno.” 

Cross must make a face, because Killer laughs and says, “you aren’t pregnant, don’t worry. but sometimes, when your lv acts up, it makes you start collecting excess magic in your tits. like you’re lactating.” 

“Great,” Cross says sarcastically, knocking his head into the wall again. 

Killer grins, completely unsarcastic. “yep. for me, because _i_ get to hear all the pretty sounds you’ll make when i _milk you dry_.” 

“And for me?” Cross questions, a little weakly from the force of Killer’s stare. 

It only feels more intense when that grin widens, and he tells Cross, “well, you wouldn’t be makin’ all those pretty noises for me if it didn’t feel nice, would you?” 

Cross nods slowly at that, and then jerkily again when Killer looks straight into his eyelights and asks, “you good to go?” 

“Please,” Cross answers, a little ashamed of how much it sounds like a whine. 

Killer hums, the satisfied sound warbling off into a quiet purr by the end, and slides his hands up to touch Cross’s breasts. He’s uncharacteristically gentle - probably, Cross thinks in the half of his mind that’s still lucid, because he’s experienced this painful, aching feeling before. 

His fingers are cool on Cross’s heated skin, fingertips pressing gently into both breasts, before he shifts to focus on the right one, nearer to him. Something warm drips onto Cross’s stomach, and he realizes after a moment that it’s his raw magic, being coaxed from his nipple by Killer’s ministrations. 

Killer shifts from the edge of the mattress to straddle Cross, and his erection presses into Cross’s waist. His hands never move from Cross’s breast, practically kneading it all the while. 

After a moment, Killer’s smile cracks wider again, and as more stored magic drips from Cross’s nipple, he swipes a few fingers over it once again. Then, he holds them up to Cross’s mouth. “wanna taste?” 

Cross stares, and then slowly opens his jaw. Killer purrs happily, leaning forward and pressing his fingers against Cross’s tongue. On Killer’s fingers, the magic had been an opaque, milky lavender, as compared to the translucent violet of its owner’s ecto-flesh. 

It barely has a taste, except for something that vaguely computes as _magic_. It’s almost too sweet, and it leaves his mouth tingling slightly. Killer hums as Cross sucks on his fingers, sucking the viscous fluid from his bones, before pulling them from Cross’s mouth with a wet sound. 

His fingers are completely clean, save for the slight, purple-tinged shine of Cross’s spit, and Cross flushes at the sight. Killer laughs at him, though it’s not mocking; there’s certainly a teasing tone in there, but the usual edge isn’t in it. 

“stars, you’re eager,” he mumbles, wiping his hand on his hoodie. “‘nd i ain’t really done anything yet - bet you’re gonna be screamin’ when i’m finished with you.” 

Cross can’t help the soft whine he releases at that; Killer sounds as full of need as Cross feels. He presses his chest towards Killer best he can, a silent plea, though it’s hampered by the weight of Killer on his waist and the unfamiliar heaviness of his breasts. 

Killer hums a long note as he replaces both hands, this time really groping, and Cross gasps. His chest is unbelievably tender, and every touch makes him more aware of it. It’s both good and bad, like the ache is both dissipating and getting worse beneath Killer’s touch. 

One hand cups the underside of his right breast, the other hovering just above it, and it’s _embarrassing_ , the way the whole thing just spills over his cupped palm. Killer must see something on his face - some nervousness or something, because Cross has never been good at hiding emotions, always been an open book - because he caresses Cross’s collarbone with his free hand, and quietly murmurs, “i got’cha, cross. always take good care of you, don’t i?” 

And Cross knows he does, because he wouldn’t trust the asshole to get him through his heats, or to even touch him in the first place if he _didn’t_. “Don’t make any cow jokes,” he grumbles weakly, the last concern he has. 

That makes Killer snort. “fine, fine. just for you, no cow jokes.” 

And then the hand on Cross’s collarbone is on his breast instead, and both hands are squeezing the ecto-flesh around his swollen nipple and it _hurts_. 

Killer leans forward, still on his lap, though that’s the last thing on Cross’s mind now. Their faces touch with a soft clack, and he distantly registers that Killer is whispering something to him, little shushing noises hushing his whimpers as he continues squeezing. 

“gonna feel better in a minute,” he promises, though it feels like the pressure lessens. One hand moves to cradle Cross’s head, keeping it from slamming into the wall again, while the other has shifted to his other breast. Killer’s hand brushes against his nipple lightly as he squeezes that one, too, and Cross vaguely registers that the other’s hand is wet with his magic. 

“that’s it,” Killer mumbles encouragingly, and it feels like he’s being more gentle this time. Or maybe Cross was just ready for it this time. Either way, when Killer’s hand disappears, Cross makes a dissatisfied noise, somewhere between a grunt and whimper. The formerly pent-up magic freely dribbles onto his torso, warm and sticky.

Killer shifts off of him, and Cross nearly reaches out with quivering hands, momentarily believing the other is leaving him. But Killer only coaxes him to lay down, to rest his head on his pillow instead of slamming it against the wall. Beside Cross’s head, and then in front of him as Killer climbs back on top of him, there’s a tell-tale red glow in the other’s shorts. 

There’s a still moment where Killer doesn’t move, simply lets his hands hover above Cross’s chest, searching his face. Cross doesn’t know what he’s looking for, but he nods, quick and shaky, and it spurs Killer to action. 

The ache is mostly gone, but Killer’s hands are somewhat wet with Cross’s magic as they return to their previous positions, one on each breast. His kneading is gentle, fingertips pressing into them repeatedly, and Cross sighs shakily. 

This time, when he gropes Cross, it actually feels _good_. A weak stream of magic follows it, and Killer mumbles, “told you, pent-up. feels better now, huh?” 

Cross whines as the touches become firmer, arching into Killer slightly. Killer’s grunts when he’s forcibly shifted, though it seems to be more from surprise than anything, because the excited anticipation in his voice is obvious when he tells Cross, “you’re gonna love this.” 

Killer takes his left nipple between his fingers, pinching hard and watching with interest as magic dribbles from the nub. His fingers twist slowly, and Cross can’t help the soft keening sound that leaves him, even as Killer chuckles at him. 

“bein’ so good,” Killer coos, hardly even teasing as he ceases his abuse of Cross’s nipple, only to grope both breasts hard. “gonna feel so much better when you’re all empty,” he promises. 

He leans down and mutters something about _fastest_ , but Cross isn’t really listening. He doesn’t think he can, especially once Killer’s teeth latch gently onto the nipple he hasn’t touched yet, fangs rolling over the nub as the magic coming from it escapes his jaw. The slow dripping stops all at once a moment later, though Cross can still feel the magic flowing from the breast Killer has his mouth on. His tongue circles the nipple there gently, lapping up Cross’s magic, and Cross belatedly puts two and two together, moaning brokenly when he realizes Killer is swallowing it. 

It takes effort to remove his clenched fingers from the comforter, but Cross manages it, gripping Killer’s shoulders tightly. Killer laughs soundlessly against him, one hand steadying the breast in his mouth, the other continuing its slow groping. He yanks at that nipple cruelly, making Cross yelp, before he lifts his head, pushing himself off of Cross slightly and smirking a bit. There’s a splotch of lavender magic - _Cross’s magic_ \- on Killer’s cheek, and Cross’s entire being burns with need. 

Killer only holds his gaze for moment, before lowering his mouth to Cross’s left breast and sucking at that nipple, too. Cross stares, and Killer meets the gaze with his own dark eye sockets. His hands creep back up to Cross’s chest from wherever they’d decided to settle, and this time when his mouth leaves Cross, his hands replace it. Killer watches his face intently, tweaking both nipples in the same back and forth motion, before pressing his hands down onto Cross’s breasts and resuming the pattern all over again. 

Cross pants and whines, no longer really capable of speaking. They’re both covered in his magic, and even as Killer pulls at his nipples, it’s still coming, however slowly. Every tug makes him hyper-aware of the warmth in his belly, and while whatever rational bit of his mind that remains is ashamed that he might cum simply from having his breasts played with, the rest of it is right there with his mouth, making incomprehensible pleas. 

Killer makes some sort of hushing noise, but Cross is babbling now, even begging, “Touch me,” though it doesn’t quite come out sounding that way. 

“‘m touchin’ you,” Killer snarks, though his tone softens as he continues, “i got’cha, criss-cross. come on,” and as he twists at Cross’s nipples slowly, watching interestedly as the other keens and arches beneath him, tells him, “cum for me, come on.” 

Cross does, and while it isn’t quite as explosive as he expected, it’s still a lot. Killer’s hands are grounding as his vision goes white for a moment, still pressing at his breasts, though less harshly than before. He pants, blearily staring up at the other, and Killer grins down at him, pinching his nipples one last time before telling him, “nice.” 

He can’t manage words, only puffs of air as he struggles to catch his breath, but Killer leans back to slip a hand into his shorts. His gaze remains on Cross, watching his face carefully, and despite the wetness in his shorts, Killer pulls his hand back out when Cross’s expression twists at a few soft touches to his clit. “wow,” he says, a little breathless himself, a pleased grin on his face. 

“Don’t,” Cross wheezes, embarrassed. 

Killer huffs soundless laugh, slipping off of Cross and telling him, “it’s a good wow.” His hand dips beneath his own waistband, exposing his cock as he continues, occasionally pausing to pant for breath as he attends to himself. “can’t believe you, hn, came in your pants from, ah, me touchin’ you.” 

Cross can’t manage a response as Killer jerks himself off, only watching the rough movement of the other’s hand on his own dick, still slicked up with _Cross’s_ excess magic. Killer cums into his hand with a groan after few long strokes, prompting Cross to mumble, “Pent-up?” 

There’s no bite to it, so Killer hardly graces it with a response, instead wiping his hand off before yanking his pants back up and flopping on top of Cross, throwing both an arm and a leg over him. Cross protests weakly, “The bed’s a mess.” 

“usually takes more than one milkin’,” Killer replies, eyes lidded. “‘s like a heat. not a one-and-done deal.” 

“I feel better,” Cross argues, though he doesn’t protest beyond an involuntary twitch when Killer’s hand makes it way to his still-manifested breast once again. 

“could always feel better than that,” Killer tells him, stroking up his side. “what’s it they say, sky’s the limit?” 

“...I don’t think that applies to orgasms,” Cross says, but he relaxes into the touch anyway. “You can consider it your reward for not making any cow jokes,” he tells Killer. 

Despite the fact that Killer has no eyelights, his sockets still seem to brighten at that, and Cross gets the sudden feeling that he’s going to end up very, very sore tomorrow.

**Author's Note:**

> twitter @avosettas


End file.
